Injection Technique for Quadrilateral Space Syndrome

Indications and Clinical Considerations

Quadrilateral space syndrome is an uncommon cause of shoulder and posterior upper arm pain first described by Cahill and Palmer in 1983. It is now encountered more frequently in clinical practice because magnetic resonance imaging (MRI) and sonography make confirmation of the clinical diagnosis much easier than with the previously required arteriography of the shoulder and upper extremity. Quadrilateral space syndrome is caused by compression of the axillary nerve as it passes through the quadrilateral space ( Fig. 47.1 ). Rarely, vascular abnormalities including aneurysmal degeneration and thrombosis of the posterior circumflex humeral artery can cause a similar clinical syndrome termed vascular quadrilateral space syndrome .

The onset of quadrilateral space syndrome is usually insidious, with the patient often not reporting any obvious antecedent trauma. The patient with quadrilateral space syndrome will report ill-defined pain in the shoulder with paresthesias radiating into the posterior upper arm and lateral shoulder. This pain and associated paresthesia will frequently be made worse with abduction and external rotation of the affected upper extremity. As the syndrome progresses, the patient may note increasing weakness of the affected arm with difficult abduction and external rotation. Most cases of quadrilateral space syndrome occur in young athletes in their early second to third decade who are involved in throwing activities. The syndrome may occasionally be seen in older patients as a result of other causes of compression of the axillary nerve as it travels through the quadrilateral space, such as glenolabral cysts, fibrous bands, or tumors ( Figs. 47.2 and 47.3 ). Mild cases of quadrilateral space syndrome will resolve over time, but more severe cases, if left untreated, will result in permanent atrophy of the deltoid and teres minor muscles.

The most important finding in patients with quadrilateral space syndrome is weakness of the supraspinatus and infraspinatus muscles. This weakness manifests itself as weakness of abduction and external rotation of the ipsilateral shoulder ( Fig. 47.4 ). With significant compromise of the axillary nerve, atrophy of the deltoid and teres minor muscle will be readily apparent on physical examination. The pain of quadrilateral space syndrome can be exacerbated by abducting and externally rotating the ipsilateral upper extremity. There often is tenderness to palpation of the quadrilateral space.

Electromyography may help identify entrapment of the axillary nerve, although the test result may be normal in mild cases even though significant neurapraxia is present. Electromyography helps to distinguish cervical radiculopathy and Parsonage–Turner syndrome from quadrilateral space syndrome. Plain radiographs are indicated for all patients with quadrilateral space syndrome to rule out occult bony disease. On the basis of the patient’s clinical presentation, additional testing including complete blood cell count, uric acid, sedimentation rate, and antinuclear antibody testing may be indicated. Both MRI and ultrasound imaging of the shoulder are indicated for all patients suspected of having quadrilateral space syndrome because these tests are highly specific for this disorder. In the rare patient in whom MRI and ultrasound imaging is nondiagnostic, subclavian arteriography to demonstrate occlusion of the posterior humeral circumflex artery may be considered because this finding is highly suggestive of a diagnosis of quadrilateral space syndrome.

Clinically Relevant Anatomy

The quadrilateral space is a 4-sided space that is bounded superiorly by the subscapularis and teres minor muscles, medially by the long head of the triceps brachii, laterally by the surgical neck of the humerus, and inferiorly by the teres major muscle (see Fig. 47.1 ). Contained within the quadrilateral space is the axillary nerve, which is a branch of the brachial plexus and the posterior circumflex humeral artery. Compromise of either of these structures by tumor, hematoma, aberrant muscle, or heterotopic bone can produce clinical symptoms.